This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to patent application Ser. No. 0000883-9 filed in Sweden on Mar. 17, 2000; the entire content of which is hereby incorporated by reference.
1. Technical Field of the Invention
This invention relates to a drilling tool of the type that comprises a shaft having a front end to which a cutting body provided with cutting edges is detachably connected by means of a screw.
2. Prior Art
Recently, it has become common to manufacture not only drilling tools but also other types of chip forming tools, such as shaft-type cutters, thread cutters and the like, from two separate components, namely on the one hand, a shaft, which most often has a long narrow, cylindrical shape, and on the other hand a cutting body provided with cutting edges which can be detachably connected to a front end of the shaft. In modern machine tools, the tool shafts are so sophisticated and expensive that they, for economic reasons, are no longer integrated with the wearing part of the tool, namely the cutting body, to form a single tool which has to be discarded when the cutting body has worn out. In other words, it is profitable to make the actual cutting body as a detachable unit, which can be replaced, while the expensive shaft may be used for a long time.
Generally, the cutting bodies of the tools are assembled on the shafts by means of screw. In certain tools, such as milling tools (see e.g, U.S. Pat. No. 5,607,263 and DE 34 48 086), simple screws are used which are screwed fast into a threaded hole in the front end of the shaft via a through hole in the cutting body. A serious disadvantage with this design, however, is that chip-forming edges cannot be formed in the center area of the front or top surface of the cutting body, and therefore the cutting body cannot be designed for drilling purposes. For this reason, previously known drilling tools having replaceable cutting bodies are structurally complicated and demand a plurality of details, such as screws, springs or drawbars for the fastening of the cutting body. This means, in practice, that the assembly as well as the disassembly of the cutting body become complicated and time-consuming at the same time as difficulties arise in centering the cutting body in relation to the shaft in an exact manner. Furthermore, the fixation becomes unreliable inasmuch as the cutting body may be dislodged from an initially centered position during operation.
The present invention aims at obviating the above-mentioned shortcomings of previously known drilling tools having replaceable cutting bodies and at providing an improved drilling tool. Therefore, a primary aim of the invention is to provide a drilling tool which with simple and few means can safeguard the cutting body of the tool on the shaft in a centered state which in a reliable manner is retained during the cutting operation. An additional aim is to create a drilling tool, the cutting body of which can be assembled and disassembled, respectively, in a simple and fast manner. Another aim is to create a drilling tool, the cutting body of which is self-centering inasmuch as the cutting body in connection with the drilling operation is brought automatically to assume the correct position also in such cases as when the cutting body is assembled initially in an incorrect manner. In one particular aspect, the invention also aims at providing a drilling tool having an improved cooling ability.
According to the invention, at least the primary aim is attained by a drilling tool comprising a rotary shaft and a cutting body detachably connected by a fastening screw in a seat formed in a front surface of the shaft. The seat includes first and second spaced-apart protrusions projecting forwardly from a bottom surface of the seat and disposed on opposite sides of a center axis of the shaft. The protrusions include respective first and second inner surfaces facing one another. The first protrusion includes a screw-threaded first hole extending into the first inner surface. The second protrusion includes a supporting shoulder projecting from an end of the second inner surface located remotely from the first protrusion. The supporting shoulder includes a first supporting surface facing generally in the same direction as the second inner surface, and a first abutment surface facing in a direction laterally of the direction in which the second inner surface faces. The abutment surface faces generally in a direction toward an end of the second protrusion located proximate the first protrusion. A distance between the second inner surface and the first supporting surface defines a thickness of the supporting shoulder. The cutting body forms a cutting edge structure and includes first and second flank parts disposed adjacent the first and second protrusions, respectively. The cutting body includes first and second outer side surfaces facing the first and second inner surfaces, respectively. The second flank part includes a recess in which the supporting shoulder is received. The recess includes a second abutment surface, and a second supporting surface respectively facing the first abutment surface and the first supporting surface. A depth of the recess is less than the thickness of the supporting shoulder, wherein the first and second supporting surfaces abut one another, and the second side surface is spaced from the second inner surface. The first flank part includes a non-threaded second hole extending therethrough and passing through the first and second side surfaces. The fastening screw extends through the second hole and is threadedly secured in the first hole. The first and second holes are slightly non-aligned wherein a tightening of the fastening screw applies a first force pressing the first inner surface and the first side surface against one another, and a second force pressing the first and second abutment surfaces against one another.
The present invention also pertains to a cutting body per se which is adapted for use in a metal-cutting drill. The cutting body comprises a top surface and a bottom surface facing in opposite directions. The top surface forms cutting edges. First and second flank surfaces extend downwardly from opposite ends of the top surface. First and second side surfaces extend downwardly from opposite sides of the top surface. Each side surface extends from the first flank surface to the second flank surface. A recess is formed in the body and is arranged to intersect both the second flank surface and the second side surface. A non-threaded through-hole extends through the cutter body from the first side surface to the second side surface and is situated closer to the first flank surface than to the second flank surface.